Auto merge of #3214 - eduardosm:move-x86-code, r=RalfJung

Move some x86 intrinsics code to helper functions in `shims::x86`

To make them reusable for intrinsics of other x86 features.

Splitted from #3192

Author: bors

src/shims/x86/mod.rs

@@ -1,3 +1,6 @@
+use rand::Rng as _;
+
+use rustc_apfloat::{ieee::Single, Float as _};
 use rustc_middle::{mir, ty};
 use rustc_span::Symbol;
 use rustc_target::abi::Size;
@@ -331,6 +334,210 @@ fn bin_op_simd_float_all<'tcx, F: rustc_apfloat::Float>(
     Ok(())
 }
 
+#[derive(Copy, Clone)]
+enum FloatUnaryOp {
+    /// sqrt(x)
+    ///
+    /// <https://www.felixcloutier.com/x86/sqrtss>
+    /// <https://www.felixcloutier.com/x86/sqrtps>
+    Sqrt,
+    /// Approximation of 1/x
+    ///
+    /// <https://www.felixcloutier.com/x86/rcpss>
+    /// <https://www.felixcloutier.com/x86/rcpps>
+    Rcp,
+    /// Approximation of 1/sqrt(x)
+    ///
+    /// <https://www.felixcloutier.com/x86/rsqrtss>
+    /// <https://www.felixcloutier.com/x86/rsqrtps>
+    Rsqrt,
+}
+
+/// Performs `which` scalar operation on `op` and returns the result.
+#[allow(clippy::arithmetic_side_effects)] // floating point operations without side effects
+fn unary_op_f32<'tcx>(
+    this: &mut crate::MiriInterpCx<'_, 'tcx>,
+    which: FloatUnaryOp,
+    op: &ImmTy<'tcx, Provenance>,
+) -> InterpResult<'tcx, Scalar<Provenance>> {
+    match which {
+        FloatUnaryOp::Sqrt => {
+            let op = op.to_scalar();
+            // FIXME using host floats
+            Ok(Scalar::from_u32(f32::from_bits(op.to_u32()?).sqrt().to_bits()))
+        }
+        FloatUnaryOp::Rcp => {
+            let op = op.to_scalar().to_f32()?;
+            let div = (Single::from_u128(1).value / op).value;
+            // Apply a relative error with a magnitude on the order of 2^-12 to simulate the
+            // inaccuracy of RCP.
+            let res = apply_random_float_error(this, div, -12);
+            Ok(Scalar::from_f32(res))
+        }
+        FloatUnaryOp::Rsqrt => {
+            let op = op.to_scalar().to_u32()?;
+            // FIXME using host floats
+            let sqrt = Single::from_bits(f32::from_bits(op).sqrt().to_bits().into());
+            let rsqrt = (Single::from_u128(1).value / sqrt).value;
+            // Apply a relative error with a magnitude on the order of 2^-12 to simulate the
+            // inaccuracy of RSQRT.
+            let res = apply_random_float_error(this, rsqrt, -12);
+            Ok(Scalar::from_f32(res))
+        }
+    }
+}
+
+/// Disturbes a floating-point result by a relative error on the order of (-2^scale, 2^scale).
+#[allow(clippy::arithmetic_side_effects)] // floating point arithmetic cannot panic
+fn apply_random_float_error<F: rustc_apfloat::Float>(
+    this: &mut crate::MiriInterpCx<'_, '_>,
+    val: F,
+    err_scale: i32,
+) -> F {
+    let rng = this.machine.rng.get_mut();
+    // generates rand(0, 2^64) * 2^(scale - 64) = rand(0, 1) * 2^scale
+    let err =
+        F::from_u128(rng.gen::<u64>().into()).value.scalbn(err_scale.checked_sub(64).unwrap());
+    // give it a random sign
+    let err = if rng.gen::<bool>() { -err } else { err };
+    // multiple the value with (1+err)
+    (val * (F::from_u128(1).value + err).value).value
+}
+
+/// Performs `which` operation on the first component of `op` and copies
+/// the other components. The result is stored in `dest`.
+fn unary_op_ss<'tcx>(
+    this: &mut crate::MiriInterpCx<'_, 'tcx>,
+    which: FloatUnaryOp,
+    op: &OpTy<'tcx, Provenance>,
+    dest: &PlaceTy<'tcx, Provenance>,
+) -> InterpResult<'tcx, ()> {
+    let (op, op_len) = this.operand_to_simd(op)?;
+    let (dest, dest_len) = this.place_to_simd(dest)?;
+
+    assert_eq!(dest_len, op_len);
+
+    let res0 = unary_op_f32(this, which, &this.read_immediate(&this.project_index(&op, 0)?)?)?;
+    this.write_scalar(res0, &this.project_index(&dest, 0)?)?;
+
+    for i in 1..dest_len {
+        this.copy_op(
+            &this.project_index(&op, i)?,
+            &this.project_index(&dest, i)?,
+            /*allow_transmute*/ false,
+        )?;
+    }
+
+    Ok(())
+}
+
+/// Performs `which` operation on each component of `op`, storing the
+/// result is stored in `dest`.
+fn unary_op_ps<'tcx>(
+    this: &mut crate::MiriInterpCx<'_, 'tcx>,
+    which: FloatUnaryOp,
+    op: &OpTy<'tcx, Provenance>,
+    dest: &PlaceTy<'tcx, Provenance>,
+) -> InterpResult<'tcx, ()> {
+    let (op, op_len) = this.operand_to_simd(op)?;
+    let (dest, dest_len) = this.place_to_simd(dest)?;
+
+    assert_eq!(dest_len, op_len);
+
+    for i in 0..dest_len {
+        let op = this.read_immediate(&this.project_index(&op, i)?)?;
+        let dest = this.project_index(&dest, i)?;
+
+        let res = unary_op_f32(this, which, &op)?;
+        this.write_scalar(res, &dest)?;
+    }
+
+    Ok(())
+}
+
+// Rounds the first element of `right` according to `rounding`
+// and copies the remaining elements from `left`.
+fn round_first<'tcx, F: rustc_apfloat::Float>(
+    this: &mut crate::MiriInterpCx<'_, 'tcx>,
+    left: &OpTy<'tcx, Provenance>,
+    right: &OpTy<'tcx, Provenance>,
+    rounding: &OpTy<'tcx, Provenance>,
+    dest: &PlaceTy<'tcx, Provenance>,
+) -> InterpResult<'tcx, ()> {
+    let (left, left_len) = this.operand_to_simd(left)?;
+    let (right, right_len) = this.operand_to_simd(right)?;
+    let (dest, dest_len) = this.place_to_simd(dest)?;
+
+    assert_eq!(dest_len, left_len);
+    assert_eq!(dest_len, right_len);
+
+    let rounding = rounding_from_imm(this.read_scalar(rounding)?.to_i32()?)?;
+
+    let op0: F = this.read_scalar(&this.project_index(&right, 0)?)?.to_float()?;
+    let res = op0.round_to_integral(rounding).value;
+    this.write_scalar(
+        Scalar::from_uint(res.to_bits(), Size::from_bits(F::BITS)),
+        &this.project_index(&dest, 0)?,
+    )?;
+
+    for i in 1..dest_len {
+        this.copy_op(
+            &this.project_index(&left, i)?,
+            &this.project_index(&dest, i)?,
+            /*allow_transmute*/ false,
+        )?;
+    }
+
+    Ok(())
+}
+
+// Rounds all elements of `op` according to `rounding`.
+fn round_all<'tcx, F: rustc_apfloat::Float>(
+    this: &mut crate::MiriInterpCx<'_, 'tcx>,
+    op: &OpTy<'tcx, Provenance>,
+    rounding: &OpTy<'tcx, Provenance>,
+    dest: &PlaceTy<'tcx, Provenance>,
+) -> InterpResult<'tcx, ()> {
+    let (op, op_len) = this.operand_to_simd(op)?;
+    let (dest, dest_len) = this.place_to_simd(dest)?;
+
+    assert_eq!(dest_len, op_len);
+
+    let rounding = rounding_from_imm(this.read_scalar(rounding)?.to_i32()?)?;
+
+    for i in 0..dest_len {
+        let op: F = this.read_scalar(&this.project_index(&op, i)?)?.to_float()?;
+        let res = op.round_to_integral(rounding).value;
+        this.write_scalar(
+            Scalar::from_uint(res.to_bits(), Size::from_bits(F::BITS)),
+            &this.project_index(&dest, i)?,
+        )?;
+    }
+
+    Ok(())
+}
+
+/// Gets equivalent `rustc_apfloat::Round` from rounding mode immediate of
+/// `round.{ss,sd,ps,pd}` intrinsics.
+fn rounding_from_imm<'tcx>(rounding: i32) -> InterpResult<'tcx, rustc_apfloat::Round> {
+    // The fourth bit of `rounding` only affects the SSE status
+    // register, which cannot be accessed from Miri (or from Rust,
+    // for that matter), so we can ignore it.
+    match rounding & !0b1000 {
+        // When the third bit is 0, the rounding mode is determined by the
+        // first two bits.
+        0b000 => Ok(rustc_apfloat::Round::NearestTiesToEven),
+        0b001 => Ok(rustc_apfloat::Round::TowardNegative),
+        0b010 => Ok(rustc_apfloat::Round::TowardPositive),
+        0b011 => Ok(rustc_apfloat::Round::TowardZero),
+        // When the third bit is 1, the rounding mode is determined by the
+        // SSE status register. Since we do not support modifying it from
+        // Miri (or Rust), we assume it to be at its default mode (round-to-nearest).
+        0b100..=0b111 => Ok(rustc_apfloat::Round::NearestTiesToEven),
+        rounding => throw_unsup_format!("unsupported rounding mode 0x{rounding:02x}"),
+    }
+}
+
 /// Converts each element of `op` from floating point to signed integer.
 ///
 /// When the input value is NaN or out of range, fall back to minimum value.
@@ -408,3 +615,81 @@ fn horizontal_bin_op<'tcx>(
 
     Ok(())
 }
+
+/// Conditionally multiplies the packed floating-point elements in
+/// `left` and `right` using the high 4 bits in `imm`, sums the calculated
+/// products (up to 4), and conditionally stores the sum in `dest` using
+/// the low 4 bits of `imm`.
+fn conditional_dot_product<'tcx>(
+    this: &mut crate::MiriInterpCx<'_, 'tcx>,
+    left: &OpTy<'tcx, Provenance>,
+    right: &OpTy<'tcx, Provenance>,
+    imm: &OpTy<'tcx, Provenance>,
+    dest: &PlaceTy<'tcx, Provenance>,
+) -> InterpResult<'tcx, ()> {
+    let (left, left_len) = this.operand_to_simd(left)?;
+    let (right, right_len) = this.operand_to_simd(right)?;
+    let (dest, dest_len) = this.place_to_simd(dest)?;
+
+    assert_eq!(left_len, right_len);
+    assert!(dest_len <= 4);
+
+    let imm = this.read_scalar(imm)?.to_u8()?;
+
+    let element_layout = left.layout.field(this, 0);
+
+    // Calculate dot product
+    // Elements are floating point numbers, but we can use `from_int`
+    // because the representation of 0.0 is all zero bits.
+    let mut sum = ImmTy::from_int(0u8, element_layout);
+    for i in 0..left_len {
+        if imm & (1 << i.checked_add(4).unwrap()) != 0 {
+            let left = this.read_immediate(&this.project_index(&left, i)?)?;
+            let right = this.read_immediate(&this.project_index(&right, i)?)?;
+
+            let mul = this.wrapping_binary_op(mir::BinOp::Mul, &left, &right)?;
+            sum = this.wrapping_binary_op(mir::BinOp::Add, &sum, &mul)?;
+        }
+    }
+
+    // Write to destination (conditioned to imm)
+    for i in 0..dest_len {
+        let dest = this.project_index(&dest, i)?;
+
+        if imm & (1 << i) != 0 {
+            this.write_immediate(*sum, &dest)?;
+        } else {
+            this.write_scalar(Scalar::from_int(0u8, element_layout.size), &dest)?;
+        }
+    }
+
+    Ok(())
+}
+
+/// Folds SIMD vectors `lhs` and `rhs` into a value of type `T` using `f`.
+fn bin_op_folded<'tcx, T>(
+    this: &crate::MiriInterpCx<'_, 'tcx>,
+    lhs: &OpTy<'tcx, Provenance>,
+    rhs: &OpTy<'tcx, Provenance>,
+    init: T,
+    mut f: impl FnMut(T, ImmTy<'tcx, Provenance>, ImmTy<'tcx, Provenance>) -> InterpResult<'tcx, T>,
+) -> InterpResult<'tcx, T> {
+    assert_eq!(lhs.layout, rhs.layout);
+
+    let (lhs, lhs_len) = this.operand_to_simd(lhs)?;
+    let (rhs, rhs_len) = this.operand_to_simd(rhs)?;
+
+    assert_eq!(lhs_len, rhs_len);
+
+    let mut acc = init;
+    for i in 0..lhs_len {
+        let lhs = this.project_index(&lhs, i)?;
+        let rhs = this.project_index(&rhs, i)?;
+
+        let lhs = this.read_immediate(&lhs)?;
+        let rhs = this.read_immediate(&rhs)?;
+        acc = f(acc, lhs, rhs)?;
+    }
+
+    Ok(acc)
+}